Loss of magnetic power

[offanon]

I recently moved from one vendor to another to manufacture solenoid cores. The specifications have not changed from the old vendor to the new vendor. The cores from the new vendor perform exceptionally well at the start of testing but after about a week of endurance testing the voltage required to latch the solenoids more than doubles. Does anyone know why this might be?

 

[pkelecy]

How is the core constructed? Steel laminations or a soft magnetic composite?

My guess, and assuming the cause is due to the core, is that the insulation layer between laminations is breaking down, allowing eddy currents to circulate. One way to check that is to measure the core temperature. If eddy currents are circulating within the core, I would expect it to heat up quite noticebly!

Good luck, and let us know what you find.

Pat

 

[offanon]

The core is solid steel, EN1A plated with low phosphorus electroless nickel plating. The solenoid runs off 30vDC.

 

[pkelecy]

Solid steel core? Well scratch my theory! I guess for a solenoid core losses must not be an issue since it's on for such a short time.

I can't think what else would cause this, at least from a magnetic standpoint, given that it worked well at the start.

Does the core also serve as a bearing surface for the plunger? If so, maybe the coating is wearing off, creating friction. Again, I'm just guessing since I don't know how this is designed.

Good luck. This is quite a mystery.

Pat

 

[dgallup]

Magnetic aging? I've read about it but never experienced it myself.

http://www.springerlink.com/content/r77v51n802522567/

Are you sure it is not some mechanical effect unrelated to the cores such as wear or friction?

 

[mac2]

Once the solenoid has reached the point where it requires twice the voltage to achieve the force you require, try reversing the 30VDC in the coil and see what happens.

 

[FeX32]

I agree with mac2.
The magnetic flux is changing the magnetic properties of the steel every time you "flip the switch".


Fe

 

[offanon]

The solenoid is mounted on a PCB so swapping the positive voltage is not so easy.
Why would the flux change the properties of the steel? Is the flux changing the ferromagnetic characteristics of the steel? Why would this happen? Perhaps some material other than low carbon steel was used?

 

[FeX32]

Any ferromagnetic material changes its magnetic properties once it is exposed to magnetic flux. The real question is how much. Some very little and some way more then we might expect.
I suspected this because of you statement "the cores from the new vendor perform exceptionally well at the start of testing but after about a week of endurance testing the voltage required to latch the solenoids more than doubles"


Fe

 

[FeX32]

Also, the permeability of the steel changes with temperature. Maybe at the end of your testing the temperature is higher.


Fe

 

[pkelecy]

A couple of other things you might try (assuming you haven't already).

1. With the solenoid off (de-energized) try moving the plunger by hand. Do the same with a new one. If it's something mechanical, you may be able to "feel" it by comparing the two.

2. Check the terminal properties of the solenoid (coil resistance and inductance). If one or the other of those have changed significantly, then that would point to a likely cause. Measure inductance with the solenoid in both open and latched positions, if possible. If the magnetic properties of the core have indeed changed, that should be evident in coil inductance.

Good luck.

Pat

 

[hacksaw]

good grief